Method for joining a jacket element and a core element together

ABSTRACT

A method for joining a highly electroconductive core element ( 2 ) to a jacket element ( 1 ) made of refined steel. In said method, the electroconductive core element ( 2 ), such as a copper bar, and the joining agent element ( 3 ) are inserted in the jacket element ( 1 ), and at least the juncture area of the elements to be joined is thermally treated, so that there is created a metallurgical joint between the electroconductive core element ( 2 ) and the refined-steel jacket element ( 1 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Application NumberPCT/FI01/00984 filed Nov. 13, 2001, and to Finnish Patent ApplicationNumber 20002523 filed Nov. 17, 2000.

BACKGROUND OF THE INVENTION

The present invention relates to a method for joining a tube element anda core element together.

The method of the invention can be applied particularly in themanufacturing of the suspension bars for electrodes, particularly forpermanent cathodes, used in the electrolysis of metals. The structure ofthe suspension bar of permanent cathodes and the joining of the platepart of the permanent cathode to the suspension bar is made problematicby the fact that in order to conduct a high electric power to the platepart, the suspension bar must contain some highly electroconductivematerial, such as copper, because acid-resistant steel has poorelectroconductivity, and consequently it cannot be the sole material ofthe suspension bar. In the patent publication WO 00/17419, there areintroduced alternative methods for manufacturing the suspension bar of apermanent cathode. These methods are typically complicated and/orrequire special devices. In arrangements manufactured according to themethods of the prior art, the electroconductive properties of the jointhave not always been maintained in a satisfactory way, especially in thecorroding conditions that prevail in the electrolytic processes ofmetals.

The object of the present invention is to realize a novel method forjoining the tube element and the core element together. Another objectof the invention is to realize a method that is economical as regards tomanufacturing technology and well suited to the targets of usage formanufacturing the suspension bar of an electrode, particularly apermanent cathode.

The arrangement according to the invention is characterized by what isset forth in the appended claims.

The arrangement according to the invention has several remarkableadvantages. By means of the method of the invention, there is achieved agood, electroconductive joint between the jacket element with a lowerelectroconductivity and the core element with a highelectroconductivity. The method is easily implemented without specialdevices. The method is suited to be applied in the manufacturing ofproducts of very different sizes and, on the other hand, in themanufacturing of varying quantities of products.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The arrangement according to the invention is explained in more detailbelow, with reference to the appended drawings, where

FIG. 1 illustrates a step of a method according to the invention priorto the welding of the second end plate, and

FIG. 2 illustrates a bar according to the invention prior to the heattreatment step.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a method for joining a highly electroconductivecore element 2 to a jacket element 1 made of refined steel. In saidmethod, the electrolytic core element 2, such as a copper bar, and thejoining agent element 3 are inserted in the jacket element 1 with apoorer electroconductivity, and at least the juncture area of theelements to be joined together is thermally treated so that there iscreated a metallurgical joint between the electroconductive core element2 and the refined-steel jacket element 1. The joining agent element 3 isessentially as long as the core element 2. Typically the joining agentelement 3 consists mainly of tin. The quantity of the joining agent 3depends on the size of the clearance between the jacket element 1 andthe core element 2, as well as on how large a part of the surfacesbetween the core element and the jacket element should be joinedtogether.

The jacket element is a tubular element with at least one end that is atleast partly closed, at least during the thermal treatment. Typicallythe first end opening of the jacket element is closed, for instance bywelding an end plate 5 thereon after the core element 2 and the joiningagent element 3 are inserted in the tube. In the embodiment according tothe drawings, also the other end opening of the jacket element is partlyclosed, for instance by welding an end plate 5 thereon after the coreelement and the jacket element are inserted in the tube. In that case anopening 7 is left at the end of the jacket element, at least for theduration of the thermal treatment. This can be achieved for instance byleaving the top edge of the welded seam 6 in the second end plate 5unwelded. Typically the elements to be joined together are kept at anessentially horizontal position during the thermal treatment. Thus thetin, while melting, can penetrate to the whole junction area. During thethermal treatment, the molten tin dissolves copper from the copper barserving as the core element 2 and creates tin bronze, whichsimultaneously begins to dissolve the inner surface of the refined steeltube serving as the jacket element 1, thus creating a metallic tinbronze joint between the core element 2 and the jacket element 1. In atypical case, the thermal treatment was carried out in a furnace, thetemperature whereof was raised essentially over about 900° C.

According to another preferred embodiment, the thermal treatment of theelements to be joined together is carried out in a position that isessentially other than horizontal. In that case that end of the jacketelement that is in a lower position is typically closed, at least up tothe height of the desired junction surfaces.

The method according to the invention is suited to manufacturing thesuspension bar of an electrode, particularly a permanent cathode. Inthis specification, the term ‘refined steel’ refers to stainless oracid-resistant steel. The term ‘copper’ refers to a material containingmainly copper, i.e. at least 50% copper.

1. A method for joining a highly electroconductive core element thatmainly consists of copper to a jacket element made of refined steel, themethod comprising inserting the electroconductive core element and ajoining element that mainly consists of tin into the jacket element, andthermally treating at least a juncture area of the elements to be joinedat a temperature sufficient to create a metallurgical joint mainly fromtin bronze between the electroconductive core element and therefined-steel jacket element.
 2. The method according to claim 1,wherein the copper core element consists of at least 50% copper.
 3. Amethod according to claim 1, wherein the joining element mainly consistsof tin.
 4. A method according to claim 1 wherein the jacket element is atube element, and at least one end thereof being at least partly closed,at least during thermal treatment.
 5. A method according to claim 1,wherein the core and jacket elements to be joined together aremaintained in an essentially horizontal position during the thermaltreatment.
 6. A method according to claim 1, wherein prior to thermaltreatment, the elements to be joined together are in a substantiallyhorizontal position, and the joining element is applied to the surfaceof the core prior to placement into the jacket element.
 7. A methodaccording to claim 1, wherein, during the thermal treatment, the coreand jacket elements are maintained in a substantially non-horizontalposition.
 8. A method according to claim 1, wherein a suspension bar ismanufactured for use with an electrode.
 9. A method according to claim 1wherein the electroconductive core element is a copper bar.
 10. A methodaccording to claim 8 wherein an electrode is a permanent cathode. 11.The method according to claim 1, wherein during the thermal treatment,molten tin from the joining element dissolves copper from the copper barto create the tin bronze metallurgical joint.
 12. The method accordingto claim 1, wherein the refined steel is stainless steel oracid-resistant steel.
 13. A method for joining a highlyelectroconductive core element to a jacket element made of refinedsteel, the method comprising: inserting the electroconductive coreelement consisting mainly of copper, and a joining agent elementconsisting mainly of tin, into the jacket element; thermally treating ina furnace at a temperature over about 900° C., at least a juncture areaof the elements to be joined to create a metallurgical joint, mainlyfrom tin bronze, between the electroconductive core element and therefined-steel jacket element.